An electronic device with an automatic backup function for handling a first data stream is provided. The electronic device comprises a main board, a data-sync chipset, a first storage unit, a wireless transmission module, and a second storage unit. Here, the data-sync chipset receives the first data stream and provides a second data stream to each of the first and second storage units so that the same file or all the files in a data-sync data folder can be stored in both the first and second storage units for the purpose of auto-backup. In addition, the wireless transmission module can transmit the first file to the second storage unit by means of wireless transmission. Accordingly, the second storage unit can be used as a mobile hard disk for wireless transmission.